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Beginner

Why does Cisco PVST+ and Rapid PVST+ insert VLAN tag into extended system ID instead of 802.1q field?

At first I thought Cisco PVST+ and Rapid PVST+ just added an 802.1q VLAN tag, but it adds it into the extended system ID instead.

 

Why did they do this? Is it because 802.1q hadn't come out at that time yet?

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VIP Collaborator

Re: Why does Cisco PVST+ and Rapid PVST+ insert VLAN tag into extended system ID instead of 802.1q field?

extendend system id is used in the root process.. for exemple:

vlan 10 = priority 32768 = 32768 + 10 = 32778
vlan 20 = priority 32768 = 32768 + 20 = 32788
Jaderson Pessoa
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VIP Advisor

Re: Why does Cisco PVST+ and Rapid PVST+ insert VLAN tag into extended system ID instead of 802.1q field?

Hi @Sam Brynes 

 

I think this discussion gives some good explanations:
https://learningnetwork.cisco.com/thread/21718

Regards

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